The invention relates to a filter for use in a fuel injection device, in particular of the type used as a final stage filter.
Final stage filters in fuel injection devices commonly take the form of xe2x80x9cedge filtersxe2x80x9d and are disposed in a fuel injector or injector adaptor to protect the finely dimensioned final stage conduits of a fuel injection device from contamination by undesirably large particles. Such particles may, for example, be the residue of internal deterioration debris, service-induced debris, or matter that has penetrated the main filter.
A fuel injection device having an edge filter typically defines a restricted passageway between a surface of the edge filter and a housing of the device in which the edge filter is disposed. Due to the restricted flow area presented to incoming fuel, an undesirable pressure drop can occur across the filter. In addition, oversize particles which are unable to pass through the restricted flow passageway are continuously represented to the entrance of the passageway. The continuous re-presenting of particles to the entrance of the passageway can cause them to be reshaped by high pressure fuel entering the passageway until they are sufficiently small in at least one dimension to pass therethrough.
Another problem which can occur in edge filters is that the housing of the filter which partially defines the restricted passageway can elastically extend so as to dilate away from the outer surface of the edge filter, thereby temporarily widening the passageway and permitting oversize contaminant particles to pass.
It is known to provide an edge filter having a plurality of filter segments arranged in a loop around the circumference of the filter. The filter segments are separated by narrow clearances which prevent oversize particulate contaminants present in the fuel from passing through the filter. High pressure forces exerted in each of the channels tend to balance each other out, thereby reducing dilation of the outer housing. The problem still exists, however, that a pressure drop can occur across the filter due to the restricted flow area.
It is an object of the present invention to provide a filter which alleviates the aforementioned problems of the prior art.
According to the present invention, there is provided a filter for a fuel injection device, the filter having a bore extending along at least a part of its length and comprising;
a plurality of channels formed in its outer surface, the channels defining, with a housing part for the filter, passages for fuel flowing from an inlet end of the filter to an outlet end of the filter, each of the channels being in fluid communication with an adjacent one of the channels by means of a clearance passage, and;
a plurality of radially extending recesses or passages formed at the inlet and outlet ends of the filter, each of the passages being in fluid communication with a channel and defining a plurality of inlet and outlet passages for fuel flowing into and out of the channels respectively.
Each of the inlet and outlet passages provides direct fluid communication with a different one of the channels such that fuel flowing in to the filter through an inlet passage and flowing out through an outlet passage must pass through at least one clearance passage prior to being discharged from the filter.
Due to the multiple number of inlet passages presented to fuel at the inlet end of the filter, the pressure drop across the filter is reduced. The provision of a plurality of clearance regions through which fuel can flow between adjacent channels also serves to minimise the pressure drop across the filter.
The clearance passages may be defined by projecting sections on the filter and the inner surface of the outer housing part, the projecting sections of the filter being radially spaced around the filter so as to separate adjacent channels.
Conveniently, the inlet end of the filter is in abutment with a collar member which defines, in part with the radially extending recesses at the inlet end of the filter, the inlet passages for fuel. Alternatively, the inlet passages for fuel may be defined solely by radially extending passages formed within the filter towards the inlet end of the filter, thus providing the advantage that the filter is a unitary part. Conveniently, the outlet passages for fuel are defined by the radially extending recesses at the outlet end of the filter in combination with a step in the outer housing.
The bore provided in the filter may include a collection zone for particles located downstream of the inlet passages. The collection zone may be provided by a permeable cupped member which permits fuel to flow therethrough at a restricted rate but which prevents the passage of particulate contaminants. This provides the advantage that reverberation effects which can occur during operation of the filter are reduced, thereby reducing particle excitation.
The provision of such a collection zone downstream of the inlet passages is advantageous in that relatively large contaminant particles which are unable to enter the inlet passages, either due to their large size or due to inertia, can be retained and deformation of such particles to allow their passage through the filter can be avoided.
The filter may be provided with a sleeve member surrounding the filter, an inner surface of the sleeve member defining, with the projecting sections on the filter, the clearance passages between adjacent channels and the outer surface of the sleeve member defining, with an inner surface of the housing part, a return passage for fuel discharged from the filter. The flow of fuel back through the return passage exerts a pressure on the sleeve member which acts against the pressure exerted by fuel flowing through the clearance passages and the restricted passages, thereby reducing dilation of the outer housing part.
According to another aspect of the invention, there is provided a filter for a fuel injection device, comprising a sleeve member surrounding the filter, the inner surface of the sleeve member defining passages for fuel flowing through the filter and the outer surface of the sleeve member defining, with an inner surface of a housing part for the filter, a return passage for fuel discharged from the filter.
The flow of fuel back through the return passage exerts a pressure on the sleeve member which acts against the pressure exerted by fuel flowing through the passages, thereby reducing dilation of the housing part. Conveniently, the sleeve member may be a cylindrical sleeve member.
According to another aspect of the invention, there is provided a fuel injection device having a housing part and a filter disposed within the housing to prevent the passage of particulate contaminants present in a fuel flow through the filter, the filter having a bore extending along at least a part of its length and comprising a plurality of channels formed in its outer surface, the channels defining, with the housing part of the filter, passages for fuel flowing from an inlet end of the filter to an outlet end of the filter, each of the channels being in fluid communication with an adjacent one of the channels by means of a clearance passage, and a plurality of radially extending recesses formed at the inlet and outlet ends of the filter, each of the recesses being in fluid communication with a channel and defining a plurality of inlet and outlet passages for fuel flowing into and out of the channels respectively.